Chemical composition of dome-shaped structures grown on titanium by multi-pulse Nd:YAG laser irradiation E. Gyo ¨rgy 1 , A. Pe ´rez del Pino, P. Serra, J.L. Morenza * Department of Physics and Optics, University of Barcelona, Avda. Diagonal 647, Barcelona E-08028, Spain Received 15 July 2003; received in revised form 9 September 2003; accepted 9 September 2003 Abstract The specific dome-shaped structures were grown by multi-pulse Nd:YAG (l ¼ 1:064 mm, t ¼300 ns, and n ¼ 30 kHz) laser irradiation of titanium targets in air at atmospheric pressure. The laser intensity values were chosen below the single-laser-pulse melting threshold of titanium. The chemical composition of the structures was studied as a function of laser pulse number as well as laser intensity, both at the outer surface layer and in depth. Micro-Raman spectroscopy, Auger electron spectroscopy (AES), and wavelength dispersive X-ray spectroscopy (WDX) were used as diagnostic techniques. Morphological investigations were performed by scanning electron microscopy. The obtained results revealed a lower oxygen concentration in the centre of the structures as compared to the borders and a lower concentration on the surface than in the depth. Moreover, it was found that the stoichiometry of the formed TiO 2x oxides increases from the structures centre towards the border and from the surface towards the depth. # 2003 Elsevier B.V. All rights reserved. PACS: 61.80Ba; 81.05.Bx; 81.65Mq; 81.70.Jb Keywords: Pulsed laser irradiation; Surface structuring; Titanium; Oxidation 1. Introduction Laser-induced oxidation of metal surfaces has both fundamental and practical interest [1]. From funda- mental point of view the process is characterised by the gradual change of the target optical properties caused by the increase of the surface temperature and oxides formation, which in turn influence the further laser energy absorption [2]. Moreover, in the materials processing industry laser assisted surface oxidation offers unique advantages over the classical thermal treatments such as the short processing time and the good spatial control, which opens the possi- bility for oxide growth in a determined area avoiding the change of the bulk materials physical properties. In particular, previous investigations were focused on oxidation of titanium targets submitted to laser irradiation and in-depth characterisation of the struc- ture and composition of the modified surface layers [3–5]. The increase of the surface absorptivity was considered to be the result of both oxygen dissolution into the metal and oxides formation. Titanium oxide surfaces attract special interest because of their Applied Surface Science 222 (2004) 415–422 * Corresponding author. Tel.: þ34-93-4021138; fax: þ34-93-4021138. E-mail addresses: engyorgy@fao.ub.es, eniko@ifin.nipne.ro (E. Gyo ¨rgy), jmorenza@fao.ub.es (J.L. Morenza). 1 On leave from Institute of Atomic Physics, P.O. Box MG. 36, Bucharest V, 76900, Romania. Tel.: þ40-14231791; fax: þ40-14231791. 0169-4332/$ – see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2003.09.010